Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with a graphical user interface showing our new design; and,

FIG. 2 is a front view of a second embodiment thereof.

In the FIGURES, the outermost broken lines show a display screen or portion thereof and form no part of the claimed design. The remaining broken lines show elements of the graphical user interface that form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 